In U.S. Pat. No. 3,982,261, issued Sept. 21, 1976, G. Antypas discloses an epitaxial layer of a quaternary III-V alloy of Ga, In, As, and P having constituents proportioned for lattice matching to a substrate having a lattice constant falling within the range of 5.45 to 6.05. The constituents of the alloy are proportioned to provide a selected bandgap energy falling within the range of 2.23 to 0.35 electron volts; corresponding to wavelengths of 0.55 to 3.5 microns.
Currently available semiconductor diode lasers that emit in the visible spectrum are typically based on the III-V quaternary InGaAlP. However, the wavelength of these lasers is no shorter than approximately 0.67 microns (red).
Currently available light emitting diodes (LEDs) are based on the III-V ternaries GaAlAs or GaAsP. These LEDs readily emit red wavelengths with high brightness and efficiency, but can reach certain yellow and green wavelengths only with relatively low efficiency. This low efficiency at wavelengths shorter than red results because emission at these shorter wavelengths is based on trap-to-band recombination and not band-to-band recombination. As a result, conventional LEDs based on ternary III-V material cannot emit or approach blue wavelengths.
Variously colored LEDs have, however, many display applications, particularly in automobiles and airplanes where brightness is important. Short-wavelength semiconductor lasers would be extremely useful in optical data storage systems to increase information density, which is inversely proportional to the square of the optical wavelength. Also, triads of red, green, and blue lasers could be used in large-screen projection for high-definition television (HDTV) systems. A further application of short-wavelength lasers, such as a blue-green laser, is as a signal carrier for underwater communications. Other applications, both commercial and military, are also feasible.
Detectors for ultraviolet (UV) and visible radiation are also important applications as are UV and visible focal-plane arrays. For example, UV imaging is important for some surveillance and tracking applications. Visible multicolor imagers competitive with existing high-performance silicon-based Charge Coupled Devices (SiCCDs) are also applications.
It is therefore an object of the invention to provide a material for use in photonic devices and capable of emission or detection of radiation at a wavelength within the entire visible spectrum.
It is another object of the invention to provide quaternary Group II-VI alloys for use in photonic devices that exhibit direct band-to-band emission within the visible spectrum.
It is another object of the invention to provide a Group II-VI quaternary alloy of Hg, Zn, S, Se that emits within the visible spectrum from violet to red, that is, within a wavelength range of approximately 750 nanometers to approximately 390 nanometers.
It is another object of the invention to provide a Group II-VI quaternary alloy of Hg, Zn, Se, Te that emits within the spectrum from green to far-infrared, that is, within a wavelength range of approximately 0.5 microns to approximately 20 microns.
It is another object of the invention to provide a Group II-VI quaternary alloy comprised of Zn, S, Se and Te; Zn, Mn, S and Se; or Hg, Cd, Zn and S.
It is a further object of the invention to provide a Group II-VI quaternary alloy that may be compositionally varied for varying the energy bandgap, and hence determining emission wavelength, while maintaining a substantially constant lattice parameter suitable for use with a substrate comprised of Group III-V material, silicon or sapphire.
It is one further object of the invention to provide a double heterojunction injection laser having an active region comprised of a Group II-VI quaternary alloy.